1. Field of the Invention
The present invention relates to a drive shaft supporting structure which can be readily mounted on a thick steel plate frame of a music box.
2. Description of the Prior Art
In general, the frame of a music box is formed by die-casting zinc alloy. However, the cost of zinc alloy die-casting occupies a large part of the material and machining cost of the music box which makes it difficult to reduce the manufacturing cost thereof. In the case of a hand-operated music box where a drive shaft is hand-turned to turn a drum, the cost of the zinc alloy die-casting occupies about 20% of the manufacturing cost of the music box.
In order to overcome the above-described drawback, the frame may be made of a thick steel plate which is about 2.5 to 3.5 mm in thickness instead of the aforementioned die-cast zinc alloy. However, such a thick steel plate has not been employed to form the frame since it is difficult to finely machine a steel plate 2.5 to 3.5 mm in thickness. In particular, it is especially hard to form a drive shaft supporting means in a thick steel plate by machining the plate. Thus, no cost advantages are obtained if a thick steel plate is used.